[PATCH] media: v4l2-async: Add waiting subdevices debugfs

[Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx>]

There is currently little to none information available
about the reasons why a v4l2-async device hasn't
probed completely.

Inspired by the "devices_deferred" debugfs file,
add a file to list information about the subdevices
that are on waiting lists, for each notifier.

This is useful to debug v4l2-async subdevices
and notifiers, for instance when doing device bring-up.

For instance, a typical output would be:

$ cat /sys/kernel/debug/video4linux/waiting_subdevices
[fwnode] 1-003c
[fwnode] 20e0000.iomuxc-gpr:ipu1_csi1_mux
[fwnode] 20e0000.iomuxc-gpr:ipu1_csi0_mux

It's possible to provide some more information, detecting
the type of fwnode and printing of-specific or acpi-specific
details. For now, the implementation is kept simple.

Also, note that match-type "custom" prints no information.
Since there are no in-tree users of this match-type,
the implementation doesn't bother.

Signed-off-by: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx>
---
 drivers/media/v4l2-core/v4l2-async.c | 54 ++++++++++++++++++++++++++++
 drivers/media/v4l2-core/v4l2-dev.c   |  5 +++
 include/media/v4l2-async.h           |  7 ++++
 3 files changed, 66 insertions(+)

diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
index e3ab003a6c85..32cd1ecced97 100644
--- a/drivers/media/v4l2-core/v4l2-async.c
+++ b/drivers/media/v4l2-core/v4l2-async.c
@@ -5,6 +5,7 @@
  * Copyright (C) 2012-2013, Guennadi Liakhovetski <g.liakhovetski@xxxxxx>
  */
 
+#include <linux/debugfs.h>
 #include <linux/device.h>
 #include <linux/err.h>
 #include <linux/i2c.h>
@@ -14,6 +15,7 @@
 #include <linux/mutex.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
+#include <linux/seq_file.h>
 #include <linux/slab.h>
 #include <linux/types.h>
 
@@ -837,3 +839,55 @@ void v4l2_async_unregister_subdev(struct v4l2_subdev *sd)
 	mutex_unlock(&list_lock);
 }
 EXPORT_SYMBOL(v4l2_async_unregister_subdev);
+
+static void print_waiting_subdev(struct seq_file *s,
+				 struct v4l2_async_subdev *asd)
+{
+	switch (asd->match_type) {
+	case V4L2_ASYNC_MATCH_CUSTOM:
+		seq_puts(s, "[custom]\n");
+		break;
+	case V4L2_ASYNC_MATCH_DEVNAME:
+		seq_printf(s, "[devname] %s\n",
+			   asd->match.device_name);
+		break;
+	case V4L2_ASYNC_MATCH_I2C:
+		seq_printf(s, "[i2c] %d-%04x\n",
+			   asd->match.i2c.adapter_id,
+			   asd->match.i2c.address);
+		break;
+	case V4L2_ASYNC_MATCH_FWNODE: {
+		struct fwnode_handle *fwnode = asd->match.fwnode;
+
+		if (fwnode_graph_is_endpoint(fwnode))
+			fwnode = fwnode_graph_get_port_parent(fwnode);
+
+		seq_printf(s, "[fwnode] %s\n",
+			   fwnode->dev ? dev_name(fwnode->dev) : "nil");
+		break;
+	}
+	}
+}
+
+static int waiting_subdevs_show(struct seq_file *s, void *data)
+{
+	struct v4l2_async_notifier *notifier;
+	struct v4l2_async_subdev *asd;
+
+	mutex_lock(&list_lock);
+
+	list_for_each_entry(notifier, &notifier_list, list)
+		list_for_each_entry(asd, &notifier->waiting, list)
+			print_waiting_subdev(s, asd);
+
+	mutex_unlock(&list_lock);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(waiting_subdevs);
+
+void v4l2_async_debug_init(struct dentry *debugfs_dir)
+{
+	debugfs_create_file("waiting_subdevices", 0444, debugfs_dir, NULL,
+			    &waiting_subdevs_fops);
+}
diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
index a593ea0598b5..8d3813e6ab56 100644
--- a/drivers/media/v4l2-core/v4l2-dev.c
+++ b/drivers/media/v4l2-core/v4l2-dev.c
@@ -14,6 +14,7 @@
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <linux/debugfs.h>
 #include <linux/module.h>
 #include <linux/types.h>
 #include <linux/kernel.h>
@@ -37,6 +38,7 @@
 		       __func__, ##arg);				\
 } while (0)
 
+static struct dentry *v4l2_debugfs_dir;
 
 /*
  *	sysfs stuff
@@ -1113,6 +1115,8 @@ static int __init videodev_init(void)
 		return -EIO;
 	}
 
+	v4l2_debugfs_dir = debugfs_create_dir("video4linux", NULL);
+	v4l2_async_debug_init(v4l2_debugfs_dir);
 	return 0;
 }
 
@@ -1120,6 +1124,7 @@ static void __exit videodev_exit(void)
 {
 	dev_t dev = MKDEV(VIDEO_MAJOR, 0);
 
+	debugfs_remove_recursive(v4l2_debugfs_dir);
 	class_unregister(&video_class);
 	unregister_chrdev_region(dev, VIDEO_NUM_DEVICES);
 }
diff --git a/include/media/v4l2-async.h b/include/media/v4l2-async.h
index d6e31234826f..312ab421aa40 100644
--- a/include/media/v4l2-async.h
+++ b/include/media/v4l2-async.h
@@ -137,6 +137,13 @@ struct v4l2_async_notifier {
 	struct list_head list;
 };
 
+/**
+ * v4l2_async_debug_init - Initialize debugging tools.
+ *
+ * @debugfs_dir: pointer to the parent debugfs &struct dentry
+ */
+void v4l2_async_debug_init(struct dentry *debugfs_dir);
+
 /**
  * v4l2_async_notifier_init - Initialize a notifier.
  *
-- 
2.29.2